A multiplicity of peptide sequences ("peptide library") will be synthesized and provided to other investigators in this NCDDG for a broad screening either in the bound form (attached to the polymeric beads) or as a mixture of peptides released to the solution just before the test. The peptide- containing beads will be identified by their affinity for a defined biological acceptor such as the EGF receptor (determined by the color reaction) after which the binding peptide will be isolated and its sequence determined in our laboratories. Peptides identified in this manner as potential ligands will be synthesized and their binding affinities and biological activities evaluated. Based on the screening information we will establish "consensus sequences" for retesting. We will also design new peptide libraries and modified peptides for further studies. Our discovery of specific peptide ligands or growth inhibitors will simplify the discovery process and aid in the design and development of antitumor drugs which could have major impact in the treatment of cancer.